Vision and self‐reported mobility performance in patients with low vision

Background: As vision plays a significant role in mobility performance, it is usual to refer low vision patients, particularly those who complain of mobility difficulties, for orientation and mobility (O&M) training to help them maintain safe independent travel. Our study aimed to determine whether there was a relationship between measures of vision and self‐reported mobility, and the applicability of a patient‐based mobility assessment in patients with heterogeneous causes of visual loss. Method: We assessed the high and low contrast visual acuity, visual field and scanning ability of 30 patients with low vision. A validated mobility questionnaire was used to assess the participants’ perceived visual ability for independent mobility. Results: Vision was significantly correlated with self‐reported mobility performance, however, visual field was a significant predictor accounting for 56.5 per cent of the variance. The instrument was well constructed with valid content and high reliability scores. Conclusions: Self‐reported mobility performance together with measures of vision could be used as a guide to refer patients for O&M training. The patient‐based assessment instrument was valid to measure perceived visual ability for independent mobility in patients with heterogeneous causes of visual loss.     

Measuring mobility performance: experience gained in designing a mobility course

Background: This paper reviews the most common methods of measuring and scoring orientation and mobility (O and M) and the effects of visual impairment on O and M. We discuss the difficulties inherent in designing a ‘real‐world’ course to measure O and M and we describe the course that we finally used. Methods: Thirty‐five participants in two age groups, with low vision due to a variety of disorders, took part in mobility trials on the final version of the course. Aspects of visual function were measured. Results: Factor analysis indicated that mobility errors, visual detection distance and visual identification distance were grouped with measures of visual acuity, contrast sensitivity and Humphrey visual field mean deviation, while preferred walking speed and walking speed were separately grouped. Humphrey pattern standard deviation did not group with any other measure and neither did percentage preferred walking speed. This study is in agreement with other studies that visual field and contrast sensitivity, sometimes with low contrast visual acuity, were the best clinical visual predictors of mobility performance. Based on our experiences we present a number of recommendations for designing courses for assessing mobility. Conclusions: For future studies, it would behove researchers to include a range of mobility measures, until further understanding is gained about how they are interrelated and contribute information on the relationship among mobility, vision and other individual factors.     

Association of visual field loss and mobility performance in older adults: Salisbury Eye Evaluation Study.

PURPOSE: To determine the association between visual field loss and orientation and mobility (O&M) performance in a population-based sample of older adults and to identify the specific regions of the visual field that are most strongly associated with O&M performance. METHODS: A population-based sample of 1504 persons between the ages of 72 to 92 was enrolled in the third round of Salisbury Eye Evaluation. Monocular visual fields (60 degrees radius) were tested with the 81-point, single intensity (24 dB) screening test strategy on the Humphrey Field Analyzer. Binocular visual fields were estimated from a combination of the monocular fields. The number of points missed was calculated for the overall visual field and for 3 non-overlapping regions: central (< or = 20 degrees radius), upper- and lower-peripheral visual fields. Orientation and mobility performance was evaluated by walking speed, number of bumps, and number of orientation errors on a circuitous, 32.8-m course seeded with obstacles. Log-linear regressions and linear regressions, adjusting for age, gender, body mass, height, cognitive and general health status, were performed. RESULTS: Loss in the overall visual field was associated with an increase in the number of bumps and decrease in walking speed. Visual field loss was not associated with the number of orientation errors. Out of the three visual field sub-regions that we tested, in terms of percentage of loss, the central and lower peripheral regions showed comparable decrements in walking speed and the central region was most strongly associated with number of bumps. CONCLUSIONS: The loss in visual field, which occurs with aging, is associated with a decline in mobility performance. Walking speed decreases, and the number of bumps into obstacles increases, with decreases in the visual field. The number of orientation errors is not associated with the loss in visual field that occurs with aging.     

Mobility performance with retinitis pigmentosa

Purpose : Reduced mobility can have a serious impact on quality of life. Though previous studies have demonstrated that some vision measures relate to the mobility of subjects with simulated and true low vision, the relationship between residual vision and mobility is not clear. We investigated the relationship between clinical vision measures and mobility performance under different illumination levels for subjects with retinitis pigmentosa (RP). Methods : Binocular visual acuities, letter contrast sensitivities and static central threshold visual fields were measured on 10 subjects with RP and nine age-matched control subjects. Mobility performance was measured on an indoor mobility course at high and low illuminances and was assessed by percentage preferred walking speed (PPWS) and number of errors. Results : The RP group showed significantly reduced PPWS and greater numbers of errors than the control group. The reduction in illumination resulted in significantly worse error and PPWS scores. Unlike the control group, the presence of a glare source did not reduce the PPWS of the RP group under high illumination. Multiple regression analyses showed that the average visual field extent was the most significant predictor of mobility; letter contrast sensitivity and visual acuity added to the regression models for the low illumination measures to account for up to 75 per cent of the variation in mobility performance. Conclusions : People with RP have worse mobility than people with normal vision, more so under reduced illumination levels. Visual field extent was the strongest predictor of mobility performance. (Clin Exp Optom 1996; 80: 1: 1–12)     

Testing night vision goggles in a dark outside environment.

BACKGROUND: People with degenerative retinal diseases such as retinitis pigmentosa, may have adequate day vision but suffer from poor night vision. We have tested newly developed night vision goggles (NVG) to help these patients overcome their night blindness, thereby promoting more opportunities for normal activities at night or in the dark. METHODS: A total of 42 subjects with night blindness due to retinitis pigmentosa, choroideremia, cone rod dystrophy, or Bardet Biedl syndrome were recruited and clinically examined (visual acuity, visual field, and contrast sensitivity). Using an experienced mobility trainer, we tested binocular NVG on the subjects in two locations: a dark room and a 1 to 2 h outside course at night that provided different levels of difficulties (i.e., obstacles, brightness, and contrast). The assessment of which patients benefited from the NVG was predominantly based on the subjective evaluation of the mobility trainer, followed by their graded responses on two questionnaires. RESULTS: Based on the evaluation of the mobility trainer, 23 (61%) of the 42 subjects experienced improved mobility and orientation with the NVG outdoors, and 19 (39%) subjects did not. The ophthalmic data demonstrated that a visual acuity better than 20/100 and a visual field > 5 degrees (Goldmann perimetry III4) is necessary to benefit from NVG usage. In addition, subjective responses on increased mobility and independence were positively correlated with successful NVG testing. CONCLUSIONS: Night vision goggles have the ability to improve poor night vision in subjects with visual acuity > 20/100 and a visual field > or = 5 degrees (Goldmann: III4). In so doing, NVG can help overcome the obstacles experienced by many people suffering from night blindness. NVG, therefore, have the potential to greatly improve quality of life.     

Vision and mobility performance of subjects with age-related macular degeneration.

PURPOSE: To investigate the effects of age-related macular degeneration (ARMD) on mobility performance and to identify the vision determinants of mobility in subjects with ARMD. METHODS: Walking speed and the number of obstacle contacts made on a 79-m indoor mobility course were measured in 21 subjects with ARMD and 11 age-matched subjects with normal vision. The mobility measures were transformed to percentage preferred walking speed and contacts score. The vision functions assessed included binocular visual acuity, contrast sensitivity, and visual field. RESULTS: In this study, subjects with ARMD did not walk significantly slower or make significantly more obstacle contacts on the mobility course than the normally sighted subjects of similar age. Between 29% and 35% of the variance in the ARMD mobility performance was accounted for by visual field and contrast sensitivity measures. The most significant predictor of mobility performance scored as percentage preferred walking speed was the size of a binocular central scotoma. CONCLUSION: As the size of a binocular central scotoma increases, mobility performance decreases.     

Age-related macular degeneration and low-vision rehabilitation: a systematic review

BACKGROUND: Because of the prevalence and devastating consequences of age-related macular degeneration (AMD), a systematic review devoted to low-vision rehabilitation and AMD seems timely and appropriate. METHODS: Several electronic databases were searched for studies from 1980 to 2006 involving individuals with low vision or visual impairment and rehabilitation interventions. Studies were assessed for quality and level of evidence. RESULTS: The findings indicate that standard low-vision rehabilitation programs, conventional in-clinic assessments, and optical devices are effective ways of managing and living with vision loss. Areas of unmet need include determining which types of orientation and mobility programs and devices are most effective and developing methods of matching assistive technologies with the individual's visual and environmental requirements. INTERPRETATION: Additional randomized controlled trials with similar intervention comparisons and outcome measures are needed to form stronger conclusions for the most effective low-vision rehabilitation interventions for individuals with AMD.     

Measures of visual function and percentage of preferred walking speed in older adults: the Salisbury Eye Evaluation Project

PURPOSE: The purpose of this study was to determine the association of static (visual acuity, visual fields, and contrast sensitivity) and dynamic (dynamic visual acuity and motion threshold) measures of vision with mobility performance on a mobility course with obstacles. METHODS: A cross-sectional population-based study of 1504 persons aged 72 to 92 years enrolled in the third round of the Salisbury Eye Evaluation Project. Standardized examinations were used to test binocular visual acuity, better eye-contrast sensitivity, visual fields, dynamic visual acuity, and motion threshold. Cognitive status was assessed by using the standardized Mini-Mental State Examination. Participants were timed when walking a straight 4-m distance and when walking through a mobility course seeded with obstacles. The percentage of preferred walking speed (PPWS) for each subject was calculated as the ratio of mobility course speed to a 4-m walking speed expressed as a percentage. RESULTS: The mean age of the participants was 78.2 years. The mean 4-m walking speed was 0.82 m/s, whereas the mean mobility course speed was 0.47 m/s. The mean PPWS was 57.1%. All vision variables except visual acuity were associated with PPWS in univariate analyses. Multivariate models found visual fields and the cognitive state to be associated with PPWS. There was no association with dynamic measures of vision. CONCLUSIONS: The mobility performance, as measured by PPWS, was associated with visual fields but not with visual acuity, contrast sensitivity, or dynamic vision measures. Deficits in cognition also play an important role in predicting mobility performance.     

Improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery

AIMS—To determine the improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery.
METHODS—Clinical vision (monocular and binocular high and low contrast visual acuity, contrast sensitivity, and disability glare), functional vision (face identity and expression recognition, reading speed, word acuity, and mobility orientation), and perceived visual disability (Activities of Daily Vision Scale) were measured in 25 subjects before and after uncomplicated cataract surgery (10 first eye surgery and 15 second eye surgery) and in 10 age matched controls.
RESULTS—Significant improvements were found after surgery in clinical and functional vision and perceived visual disability. Greater improvements were found after first eye surgery than after second eye surgery. However, first eye surgery did not return all scores to age matched normal levels. There were significant improvements in several of the tests measured after second eye surgery, and all postoperative values were similar to those from age matched normals.
CONCLUSIONS—Significant improvements in clinical, functional, and perceived vision are obtained by cataract surgery. The improvements in objective measures of functional vision found in this study support previous findings of improvements in patients' perceived functional vision. In addition, these data provide support to the necessity of second eye surgery in some patients to improve certain aspects of visual function to age matched normal levels.

     

Mobility performance in glaucoma.

PURPOSE: To determine whether glaucoma affects mobility performance and whether there is a relationship between mobility performance and stage of disease as estimated from vision-function measures. METHODS: The mobility performance of 47 glaucoma subjects was compared with that of 47 normal-vision subjects who were of similar age. Mobility performance was assessed by the time required to complete an established travel path and the number of mobility incidents. The subjective assessment of falling and fear of falling were also compared. Vision function was assessed by measures of visual acuity, contrast sensitivity, monocular automated threshold perimetry, and suprathreshold; binocular visual fields were assessed with the Esterman test. RESULTS: The glaucoma subjects walked on average 10% more slowly than did the normal-vision subjects. The number of people who experienced bumps, stumbles, or orientation problems was almost twice as high in the glaucoma group than the normal-vision group, but the difference did not reach statistical significance. The difference between groups also was not significant with respect to the number of people who reported falling in the past year (38% for the glaucoma group and 30% for the normal-vision group) or a fear of falling (28% for the glaucoma group and 23% for the normal-vision group). The visual fields assessed with a Humphrey 24-2 test were more highly correlated with walking speed in glaucoma than the visual fields scored by the Esterman scale or than visual acuity or contrast sensitivity. CONCLUSIONS: Glaucoma is associated with a modest decrease in mobility performance. Walking speed decreases with severity of the disease as estimated by threshold perimetry.     

New Systematic Review Methodology for Visual Impairment and Blindness for the 2010 Global Burden of Disease Study

Abstract

Purpose: To describe a systematic review of population-based prevalence studies of visual impairment (VI) and blindness worldwide over the past 32 years that informs the Global Burden of Diseases, Injuries and Risk Factors Study.

Methods: A systematic review (Stage 1) of medical literature from 1 January 1980 to 31 January 2012 identified indexed articles containing data on incidence, prevalence and causes of blindness and VI. Only cross-sectional population-based representative studies were selected from which to extract data for a database of age- and sex-specific data of prevalence of four distance and one near vision loss categories (presenting and best-corrected). Unpublished data and data from studies using rapid assessment methodology were later added (Stage 2).

Results: Stage 1 identified 14,908 references, of which 204 articles met the inclusion criteria. Stage 2 added unpublished data from 44 rapid assessment studies and four other surveys. This resulted in a final dataset of 252 articles of 243 studies, of which 238 (98%) reported distance vision loss categories. A total of 37 studies of the final dataset reported prevalence of mild VI and four reported near VI.

Conclusion: We report a comprehensive systematic review of over 30 years of VI/blindness studies. While there has been an increase in population-based studies conducted in the 2000s compared to previous decades, there is limited information from certain regions (eg, Central Africa and Central and Eastern Europe, and the Caribbean and Latin America), and younger age groups, and minimal data regarding prevalence of near vision and mild distance VI.     

The prevalence and incidence of visual impairment in people of age 20–59 years in industrialized countries: A review

BACKGROUND Reviews on the prevalence of blindness and low vision in persons of age 20 to 59 years are lacking. We have therefore carried out a review based on a Medline search. METHODS The review was confined to epidemiological studies performed in Western Europe, North America and Australia covering the age group 20 to 59 years where there were comparable definitions of blindness and low vision according to the IAPB and WHO classification of blindness and low vision. RESULTS Three surveys, four register studies and two studies based on multiple sources matched our selection criteria. Blindness and low vision are described separately. Blindness Only one study, based on multiple sources, covered the whole age group 20 to 59 years. In this study the overall prevalence of blindness was 0.08%. The prevalence of blindness was 0.04% among those 20–39 years old, whereas in the age group 40–59 years it was 0.1% in two surveys and one study on multiple sources. However, the prevalence was higher, 0.5% among whites and 0.7% among colored, in The Baltimore Eye Study. The definition of blindness was similar in all three studies. Low vision Three studies provided data on the prevalence of low vision in the age group 20–59 years, although the number of cases was very small. In one study the prevalence of a visual acuity =6/24 to 6/48 was 0.07% and in another the prevalence was 0.17% using &lt;6/18 to 0.5/60. No person with low vision was found in the third study. CONCLUSIONS The existing epidemiological data on blindness and low vision among adults aged 20 to 59 years are insufficient. Epidemiological studies based on multiple sources are needed for the study of rare conditions such as blindness and low vision.     

Simulating prosthetic vision: II. Measuring functional capacity

Investigators of microelectronic visual prosthesis devices have found that some aspects of vision can be restored in the form of spots of light in the visual field, so-called “phosphenes”, from which more rich and complex scenes may be composed. However, questions still surround the capabilities of how such a form of vision can allow its recipients to “see” and to carry out everyday activities. Through simulations of prosthetic vision, researchers can experience first-hand many performance and behavioral aspects of prosthetic vision, and studies conducted on a larger population can inform the performance and behavioral preferences in general and in individual cases. This review examines the findings from the various investigations of the functional capacity of prosthetic vision conducted through simulations, especially on the topics of letter acuity, reading, navigation, learning and visual scanning adaptation. Central to the review, letter acuity is posited as a reference measurement so that results and performance trends across the various simulation models and functional assessment tasks can be more readily compared and generalized. Future directions for simulation based research are discussed with respect to designing a functional visual prosthesis, improving functional vision in near-term low-phosphene-count devices, and pursuing image processing strategies to impart the most comprehensible prosthetic vision.     

Mobility and low vision: a review

Theories of mobility have been developed mainly with respect to mobility of the totally blind. How the normally sighted or the partially sighted are able to use visual information to move about in the world is not well understood. Whether the cues used by the sighted are the same as those used by the partially sighted in achieving mobility is not known. Thus the performance measures which are used have been developed on an ad hoc basis and may not be the best measures available for assessment of mobility or improvement in mobility in the partially sighted. The most important factors in mobility of the partially sighted have not been identified. They must be specified so that advice and training can be directed toward the most effective steps these patients can take in using their residual vision to achieve independent mobility.     

Prevalence of blindness and low vision: a study in the rural Heilongjiang Province of China

Background: The prevalence of blind individuals in the north of China is unknown. The study aimed to investigate the prevalence and causes of blindness and low vision in rural areas in Heilongjiang province of China in 2008–2009. Design: Cross‐sectional study. Participants or Samples: A cluster random sampling method was used to recruit participants of all ages in rural areas of Heilongjiang. Methods: Trained professionals performed interviews and clinical examinations to measure visual acuity. The relationships between blindness or low vision and age, gender and education level were analysed. Main Outcome Measures: The main outcome measure was prevalence rates of bilateral blindness and bilateral low vision. Results: Of the 11 787 subjects, 10 384 (88.1%) were surveyed. The overall age‐adjusted prevalence rates were 0.7% (95% confidence interval: 0.5–0.8%) for bilateral blindness and 1.7% (95% confidence interval: 1.4–1.9%) for bilateral low vision. The prevalence rates of blindness and low vision were higher in the elderly and uneducated population (P < 0.05). The main causes for blindness and low vision were cataracts (44.1 and 46.0%, respectively) and refractive errors (17.7 and 42.5%, respectively). Conclusion: Blindness and low vision are highly prevalent among people with cataracts and refractive errors. Eye care planning must focus on treating the avoidable and curable forms of blindness.     

Contribution of vision variables to mobility in age-related maculopathy patients

Can mobility performance be predicted from measures of vision function? This study addressed this question by measuring a series of vision variables including visual acuity, visual fields, and differential motion sensitivity in a group of patients with age-related maculopathy (ARM) and a group of age-matched normals. Mobility performance at three adaptation levels was determined objectively on an indoor course. The results indicate that for the patients with ARM, mobility variables can be predicted from measures of vision function, including differential velocity sensitivity, and that simple variables such as time taken to complete the course and average speed are those which relate best to vision.     

Does mobility performance of visually impaired adults improve immediately after orientation and mobility training?

BACKGROUND: Previous studies that have attempted to determine the effect of orientation and mobility training on mobility performance of visually impaired adults have had a number of limitations. With the inclusion of a control group of subjects, this study investigated the effect of orientation and mobility training on mobility performance of a group of visually impaired adults. METHODS: Vision was measured binocularly as high- and low-contrast visual acuity, letter and edge contrast sensitivity, and Humphrey kinetic visual fields. The subjects' mobility performance was assessed as percentage preferred walking speed (PPWS) and error score before and after mobility training. RESULTS: Orientation and mobility training did not enhance mobility performance compared with the control group, who did not receive training, when performance was measured immediately after training. PPWS improved for both groups with short-term practice only, but there was no improvement in error score due to either practice or training. CONCLUSIONS: There was no immediate improvement in mobility performance of visually impaired adults after orientation and mobility training. Familiarity with the route may play an important role in measured improvement of mobility performance after orientation and mobility training.     

Improvements in clinical and functional vision and quality of life after second eye cataract surgery.

PURPOSE: To determine whether there is a need for second eye cataract surgery or whether cataract surgery in one eye provides sufficiently adequate vision. METHODS: The vision of 43 patients was assessed using a battery of clinical vision tests, performance-based functional vision tests, and quality of life questionnaires, both before and a few months after cataract surgery. Twenty-five patients underwent second eye surgery and 18 patients underwent first-eye surgery. To determine whether cataract surgery returned vision to normal levels, a control group of 25 subjects of a similar age with normal, healthy eyes was also assessed. RESULTS: Overall, greater improvements occurred in most aspects of vision after first eye surgery than after second eye surgery. However, second eye surgery provided similar improvements in mobility orientation and self-reported night driving to those after first eye surgery, and substantially greater improvements in stereoacuity and reductions in anisometropia. CONCLUSIONS: The study provides additional evidence to support the need for second eye cataract surgery. Second eye surgery may be particularly important to improve mobility orientation and the avoidance of falls.     

Measuring outcomes of vision rehabilitation with the Veterans Affairs Low Vision Visual Functioning Questionnaire

PURPOSE: To evaluate the sensitivity to change, in patients who undergo vision rehabilitation, of the Veteran Affairs (VA) Low Vision Visual Functioning Questionnaire (LV VFQ-48), which was designed to measure the difficulty visually impaired persons have in performing daily activities and to evaluate vision rehabilitation outcomes. METHODS: Before and after rehabilitation, the VA LV VFQ-48 was administered by telephone interview to subjects from five sites in the VA and private sector. Visual acuity of these subjects ranged from near normal to total blindness. RESULTS: The VA LV VFQ exhibited significant differential item functioning (DIF) for 7 of 48 items (two mobility tasks, four reading tasks, and one distance-vision task). However, the DIF was small relative to baseline changes in item difficulty for all items. Therefore, the data were reanalyzed with the constraint that item difficulties do not change with rehabilitation, which assigns all changes to the person measure. Subjects in the inpatient Blind Rehabilitation Center (BRC) program showed the largest changes in person measures after vision rehabilitation (effect size = 1.9; t-test P < 0.0001). The subjects in the outpatient programs exhibited smaller changes in person measures after rehabilitation (effect size = 0.29; t-test P < 0.01). There was no significant change in person measures for the control group (test-retest before rehabilitation). CONCLUSIONS: In addition to being a valid and reliable measure of visual ability, the VA LV VFQ-48 is a sensitive measure of changes that occur in visual ability as a result of vision rehabilitation. Patients' self-reports of the difficulty they experience performing daily activities measured with this instrument can be used to compute a single number, the person measure that can serve as an outcome measure in clinical studies. The VA LV VFQ-48 can be used to compare programs that offer different levels of intervention and serve patients across the continuum of vision loss.     

Measuring the Personal Burden of Eye Disease and Vision Impairment

Purpose: To describe research methods for assessing the personal burden of eye disease and vision impairment on health and functional well-being. Methods: Three methods are described, which are largely complementary of each other. (1) Questionnaires are patient-centered in that they provide the person's own self-reported perspective on difficulty in engaging in everyday activities, psychological well-being, and/or health status. Examples are generic and vision-targeted health-related quality of life instruments, domain-specific questionnaires, and instruments that screen for psychological comorbidities. (2) Direct assessment of actual behavior provides information about the functional competences the patient has. Examples are mobility performance and reading speed. (3) Administrative records maintained by government, healthcare, and other agencies provide information relevant to the existence of adverse or detrimental circumstances that engender decreased health and well-being. Examples are healthcare utilization, employment history, and motor vehicle collision involvement. Discussion: Measures of eye disease severity should not be used in research as surrogates for the personal burden of eye disease and vision impairment. Individuals personally respond to and cope with the presence of eye disease and vision impairment in very wide ranging ways. There are several ways to measure the personal burden of eye disease and vision impairment that provide information about the person's own perspective on his/her health and well-being and functional competences.